I've had this piece for awhile, and I feel quite comfortable posting about it now. This piece is godly for any Dragoon that likes to /mage, and even for those that like to go pure /melee.
Test:
/Melee:Wyvern has to be at full(100%, no less) HP most of the time for the breath to deal full damage, but this is with no Strafe merits and no wyvern HP+ gear... 210 is the average breath my wyvern does with this piece on, and doubles exactly when using Deep Breathing: 420, very nice magic damage, and if you can close light and get it to MB, you do even more :D
/Mage:Wyvern HP can be anywhere from full to 1HP, and there will not be a difference in Healing Breath potency. Wyvern HP gear GREATLY increases the amount your breaths heal, my Minimum with no TP, no WyvHP, and no Deep Breathing: 364. Maximums with 300% TP, and using as much WyvHP gear i could get my hands on: 465. The average cure with WyvHP gear on without TP is about 412HP, thats more than enough to compete with Cure IV, and it only cost us 5-10MP. But with Deep Breathing, you can also give this a Divine Seal effect, and double the potency. Also, i've been hearing that Strafe merits add about 15HP to your cures per upgrade, very worth it if you plan to sub mage a lot
If you have any more questions feel free to ask, I may not have covered everything in this, but i plan to get Strafe merits and i'll let you know how it turns out. As for the rest of you Dragoons out there that don't have this piece yet, don't think it impossible, it just take a lot of time and effort, which is well worth the ability to say you are one of the most potent and efficient healers in the game.